I'm running the fel pro composite gaskets on my car making 17.5 psi of boost (ported heads, larger valves, larger cam) and making over 300rwhp with no issues. I'm actually going to be upping the boost another pound or so now that I've got a bigger cam in. I'm estimating I'm going to be about 350rwhp.
I believe it has alot to do with managing the detonation these motors have. Stupid things like running 32 degrees of timing with the knock sensor turned off is going to blow head gaskets, and MLS will not save you there. Other dumb things like running 25% OD on a stock blower with a stock IC, stock heads and cam and no tune is going to blow gaskets... and I can add a bunch of other reasons.
It was mentioned earlier how MLS can handle the heads lifting and reseal.... Sure they will reseal, sort of, but count on redoing the gaskets as soon as possible, as they will not totally 100% seal up again. Ask some of the guys that have had that happened to them.
The stock SC motor detonates, especially in cooler weather, and I strongly believe thats what kills the head gaskets after a couple of 100000 miles, which to me isn't all that bad considering what these motors are trying to do.
I mean look at it this way. People are calling these motors absolute crap and screaming switch to v8 because they are more reliable etc. Well, you know what? Lets see what a factory built 5.0L (I'll allow updated with factory built forged internals) will look like with 13 pounds of boost on it that has constant detonation after a couple of 100000 miles on it
. I don't see race built motors being asked to go for 200000 miles in all different aspects of driving conditions out there without a rebuild.
I also like the idea that the head gaskets do blow out, because if something goes wrong, its alot cheaper to replace those than having to replace the whole motor because something else gave way, which usually is catastrophic.
MLS gaskets are better ultimately if you can afford all the work thats involved... but if you are responsible with modding the motor and what you do with it, then the composites will do you good.
Fraser